State-of-the-art upper limb prostheses are severely limited in their ability to provide sensory feedback to a user. The lack of sensory feedback forces prosthesis users to rely on visual feedback alone in manipulating objects, and often leads to abandonment of the prosthesis in favor of the user's unimpaired arm. Consequently, there is a critical need to develop mechanisms that enable people with upper limb amputations to be able to receive sensory feedback from the environment. Through the use of techniques like targeted reinnervation, there has been significant progress in providing patients with intuitive neural control of their prostheses as well as sensory feedback. Studies have shown that patients receiving sensory stimulation over reinnervated sites while operating a prosthesis more strongly incorporate the artificial limb into their body schema. However, there is limited cutaneous space available over the reinnervated sites for both EMG sensors and stimulators to be placed. As a result, the overall objective of the proposed research is to clinically evaluate a flexible, stretchable epidermal electronic device that conforms to the skin and can simultaneously record EMG and provide electrotactile sensory stimulation at high density over reinnervated sites. We hypothesize that long-term, closed-loop sensorimotor control in prostheses enabled by epidermal electronics will improve fine motor control and promote incorporation of the prosthesis into the body schema, ultimately reducing prosthesis abandonment. We will address this hypothesis through the following Specific Aims, in which I will 1) Optimize and validate a single flexible epidermal device that can both acquire EMG and provide electrical stimulation simultaneously at high density, 2) develop methods for automatic calibration and modulation of electrotactile sensation intensity to enable long-term wear, and 3) improve fine force control, object recognition, and embodiment through the use of sensory feedback. In turn, we expect that daily usage of prosthetic devices will increase due to the incorporation of high resolution sensory feedback. With the training environment provided by Dr. Levi Hargrove at the Rehabilitation Institute of Chicago, and Dr. Timothy Bretl and Dr. John Rogers the University of Illinois at Urbana-Champaign, we will be able to effectively enable long-term, closed-loop upper limb sensorimotor prosthetic control through the use of epidermal electronic devices.